Effect of high pressure treatment on the aging characteristics of Chinese liquor as evaluated by electronic nose and chemical analysis

Distilled beverage aging: A review on aroma characteristics, maturation mechanisms, and artificial aging techniques

The market value of distilled beverage relies on its quality with a major contribution of distinctive and fascinating aromas. The aroma of distilled beverage is built on the basis of chemical components and can be modified through a series of physical and chemical processes such as aging. Revealing the hidden knowledge behind the evolution of numerous chemical components during these physicochemical processes in distilled beverages is not only significant but also challenging due to its complex system. In this review, the trends in the changes of associated aroma compounds over aging are proposed on the basis of understanding the relationship between chemical components and aroma profiles of numerous typical distilled beverages. The different aging systems, both classical platforms from Eastern countries (pottery jars) to Western countries (wood barrels), and modern platforms such as artificial aging technologies are outlined and compared with their respective applications. Optimizing aging processes is a challenging but imperative step, which warrants further fundamental knowledge from targeting aging-related molecules to the exploration of multitude physicochemical reaction mechanisms that occur during this process, such as the formation of potent odorant compounds in specific containers and environments, as well as mass transfer processes between solid and liquid interfaces. Understanding these maturation mechanisms of distilled beverages expressed by chemosensory signature holds promise for major improvements in future aging technologies that can efficiently yield stable and high-quality products.

Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GC×GC-TOFMS) in conventional and reversed column configuration for the investigation of Baijiu aroma types and regional origin

Baijiu is a traditional Chinese spirit with an extraordinarily rich pattern of volatile compounds resulting from the microflora involved in fermentation, as well as the complexity of technological process. Comprehensive two-dimensional gas chromatography in the conventional and reversed column setups (non-polar - polar and polar - non-polar columns) was tested for its ability to differentiate Baijiu samples in terms of their aroma and origin (region). A total of 65 Baijiu samples were used for the study and volatile compounds were extracted by SPME with a subsequent analysis by GC×GC-TOFMS. Orthogonality of both setups was compared, so was the number of compounds identified using each setup. Repeatability of compound groups for the conventional and reversed column setups was compared; moreover, multiblock orthogonal component analysis (MOCA) was used to visualize data sets. OPLS-DA was used for Baijiu classification. Both column setups provided excellent discrimination of the Light, Soy sauce, Feng and Herbal aromas. A better classification result for the Strong and Jian aromas was recorded for the conventional column setup. Within the Strong aroma using OPLS-DA both column setups provided perfect abilities to discriminate Baijiu from the Sichuan, Heilongjiang and Jiangsu regions. Two validation methods were applied in the classification models - all the predictive abilities evaluated by the internal validation were further confirmed by the external validation.

Evolution of the key odorants and aroma profiles in traditional Laowuzeng baijiu during its one-year ageing

Changes of key odorants and aroma profiles of Chinese Laowuzeng baijiu during its one-year ageing were determined by HS-SPME-AEDA and direct injection-AEDA (DI-AEDA). Ethyl hexanoate, (E,E)-2,4-decadienal, and 2-phenylethyl acetate showed the highest FD value (486) in all ageing stages. With regards to aroma profiles, fruity, floral, acidic, sweet/honey and cheesy aromas were enhanced during storage, while pickled vegetable, grain and alcoholic notes weakened during the ageing. Quantitation and OAVs showed that most of the aroma compounds (OAVs > 1), including ethyl esters, aldehydes, and acids, increased their contents within the same period, whereas nonanal, 2-phenylethyl acetate, ethyl benzoate, 4-ethylguaiacol, propanol and 3-methyl-1-butanol decreased in content after the storage of 365 days. Simulated aged samples, in which fresh samples were spiked with 18 compounds, were examined by triangle tests, which indicated that the "fruity" compounds were crucial for maintaining the special aroma profile of an aged sample.

Compositional Differences and Similarities between Typical Chinese Baijiu and Western Liquor as Revealed by Mass Spectrometry-Based Metabolomics

Distilled liquors are important products, both culturally and economically. Chemically, as a complex mixture, distilled liquor comprises various chemical compounds in addition to ethanol. However, the chemical components of distilled liquors are still insufficiently understood and compositional differences and similarities of distilled liquors from different cultures have never been compared. For the first time, both volatile organic compounds (VOCs) and non-VOCs in distilled liquors were profiled using mass spectrometry-based metabolomic approaches. A total of 879 VOCs and 268 non-VOCs were detected in 24 distilled liquors including six typical Chinese baijiu and 18 typical Western liquors. Principal component analysis and a correlation network revealed important insights into the compositional differences and similarities of the distilled liquors that were assessed. Ethyl esters, a few benzene derivatives, and alcohols were shared by most distilled liquors assessed, suggesting their important contribution to the common flavor and mouthfeel of distilled liquors. Sugars and esters formed by fatty alcohol differ significantly between the assessed Chinese baijiu and Western liquors, and are potential marker compounds that could be used for their discrimination. Factors contributing to the differences in chemical composition are proposed. Our results improve our understanding of the chemical components of distilled liquors, which may contribute to more rigorous quality control of alcoholic beverages.

Effect of high pressure treatment and short term storage on changes in main volatile compounds of Chinese liquor

Changes in main volatile compounds of Chinese liquor after high pressure (HP) treatment and following short term storage were investigated. 400 MPa-15 min & 400 MPa-30 min were applied to young liquor. Results from gas chromatography (GC) analysis revealed decreasing trends in alcohols, aldehydes and ethyl acetate immediately after HP treatments, which was in consistent with those in natural aging process; but no significant change was found in acids. However, differences in main volatile compounds between young liquor and pressurized liquors disappeared after two to six months of storage. Principal component analysis (PCA) performed well in presenting overall differences among all liquor groups, which verified our previous findings in GC analysis. This research broadened the knowledge of HP processing on distilled alcoholic beverages and provided an alternative technique for liquor quality modification.

Quality assessment of Chinese liquor with different ages and prediction analysis based on gas chromatography and electronic nose

The economic value of Chinese liquor is closely related with its age. Results from gas chromatograph (GC) analysis indicated that 8 dominant compounds were decreased with the increase of liquor age (0 to 5 years) while ethyl lactate was found to be the most stable dominant compound as no significant change was observed in it during the aging process. Liquor groups with different ages were well-discriminated by principal component analysis (PCA) based on electronic nose signals. High-accurate identification of liquor ages was realized using linear discriminant analysis (LDA) with the accuracy of 98.3% of the total 120 samples from six age groups. Partial least squares regression (PLSR) exhibited satisfying ability for liquor age prediction (R²: 0.9732 in calibration set and 0.9101 in validation set). The feasibility of volatile compounds prediction using PLSR combined with electronic nose was also verified by this research. However, the accuracies of PLSR models can be further promoted in future researches, perhaps by using more suitable sensors or modeling approaches.

Characterization of Chinese liquor aroma components during aging process and liquor age discrimination using gas chromatography combined with multivariable statistics

Chinese liquor aroma components were characterized during the aging process using gas chromatography (GC). Principal component and cluster analysis (PCA, CA) were used to discriminate the Chinese liquor age which has a great economic value. Of a total of 21 major aroma components identified and quantified, 13 components which included several acids, alcohols, esters, aldehydes and furans decreased significantly in the first year of aging, maintained the same levels (p > 0.05) for next three years and decreased again (p < 0.05) in the fifth year. On the contrary, a significant increase was observed in propionic acid, furfural and phenylethanol. Ethyl lactate was found to be the most stable aroma component during aging process. Results of PCA and CA demonstrated that young liquor (fresh) and aged liquors were well separated from each other, which is in consistent with the evolution of aroma components along with the aging process. These findings provide a quantitative basis for discriminating the Chinese liquor age and a scientific basis for further research on elucidating the liquor aging process, and a possible tool to guard against counterfeit and defective products.